As a type of fluid control valve, a fluid control valve disclosed in JP 2015-014331A (Reference 1) has been known. As illustrated in FIG. 2 of Reference 1, the fluid control valve (air pressure regulating valve 4) includes: a valve housing 41 formed with a flow path (including a pressure regulating valve inlet 411d, a pressure regulating valve outlet 411e, and a flow path R1) having an inflow port and an outflow port for a fluid; a valve seat (pressure regulating valve seat 411f) formed in the flow path; a driving device (motor assembly 42) mounted in the valve housing; a valve stem (valve shaft 44) moved by being operated by the driving device; a valve body (valve member 45) mounted on the valve stem and configured to open and close the flow path by being separated from or brought into contact with the valve seat; and a diaphragm 46 configured to be moved together with the valve body and having an outer circumferential portion sealably fixed to the valve housing, in which one side of the diaphragm faces a fluid chamber 414 that includes the flow path and the valve seat so as to allow the fluid to flow therein, and the other side of the diaphragm faces an atmosphere chamber (air chamber) 415 that inhibits the infiltration of a fluid thereinto and is opened to the atmosphere. An inner circumferential portion of the diaphragm (a circumferential edge of a mounting hole 461 of the diaphragm 46) is clamped in an up and down direction by a spring retainer 453 and a diaphragm holding body 455 which are fixed to a valve frame 451 mounted on the valve stem at a position spaced apart from an outer circumference of the valve stem outward in a radial direction of the valve stem, and the inner circumferential portion of the diaphragm is fixed between the spring retainer 453 and the diaphragm holding body 455 in a liquid-tight manner. In addition, a seal member (O-ring 454), which exhibits a sealing function and prevents moisture, a foreign matter, or the like, which has infiltrated into the fluid control valve, from infiltrating into the atmosphere chamber defined by the diaphragm, is provided between the valve frame 451 and the spring retainer 453.
However, in the aforementioned configuration, the inner circumferential portion of the diaphragm is clamped in the up and down direction by the spring retainer 453 and the diaphragm holding body 455 fixed to the valve frame 451 mounted on the valve stem at the position spaced apart from the outer circumference of the valve stem outward in the radial direction of the valve stem, and the inner circumferential portion of the diaphragm is fixed between the spring retainer 453 and the diaphragm holding body 455 in a liquid-tight manner, and as a result, the inner diameter of the diaphragm is inevitably increased, whereby the dimension of an outer diameter of the fluid control valve is enlarged. In addition, the dedicated seal member (O-ring 454), which prevents moisture, a foreign matter, or the like, which has infiltrated into the fluid chamber in the fluid control valve, from infiltrating into the atmosphere chamber defined by the diaphragm, needs to be provided separately from the diaphragm.
Thus, a need exists for a fluid control valve which is not susceptible to the drawback mentioned above.